Field of the Invention
The present invention relates to a data transmission apparatus that is connected with digital and/or analog signal sources.
In general, when a digital signal is used in data transmission its reliability can be improved with ease by the addition of a so-called error correcting code, such as a cyclic redundancy check code (CRC), a parity code or the like. Also, a bus-line system in which one line can be commonly utilized by a plurality of systems can be effected with ease.
In the case of an analog transmission in which the information is provided by voltage values or the like, there are drawbacks in that attenuation thereof is proportional to the transmission distance and the analog transmission system is susceptible to noise. Also, the analog transmission system cannot utilize means for improving a reliability, such as the CRC code, a parity code or the like. Therefore, the analog transmission system is not too suitable for long distance data transmission. Nevertheless, the analog transmission system can transmit data of a plurality of levels in addition to binary data of "1" and "0" in the digital signal transmission and is considered an effective means in short distance transmission.
The assignee of the present application has previously proposed an apparatus in which a memory integrated circuit (IC) is mounted inside of a magnetic tape cassette used in a VTR and a circuit board having an electrical contact is also formed therein. When such magnetic tape cassette is loaded in the VTR, the contact is brought in contact with a detection terminal of the VTR, so that inherent information relating to in the cassette that is stored in the memory IC (tape length, tape remaining amount, the number of times that the tape has been used, rental tape identity, or other tape information concerning record contents, such as table of contents, etc.) can be read out. Then, such information is displayed and operation of the VTR is controlled accordingly (see Japanese patent application No. 4-165444). In this case, information is read out from the VTR in a digital fashion.
Further, the assignee of the present application has previously proposed an apparatus in which a circuit board having similar contacts formed thereon is mounted on a magnetic tape cassette used in a VTR. When the contacts are short-circuited, opened or connected via resistors, the VTR can determine these conditions of the contacts so that the VTR side can detect and employ various information (tape thickness, kinds of magnetic materials, etc.) inherent in the magnetic tape cassette (Japanese patent application No. 4-209470). That is to say, the information discrimination can be carried out in an analog fashion.
When there are present a magnetic tape cassette from which information must be read out in a digital fashion and a magnetic tape cassette which must be discriminated in an analog fashion, the VTR must discriminate them satisfactorily and read out information from the magnetic tape cassette in a digital fashion or discriminate such magnetic tape cassette in an analog fashion. This requirement for a VTR to deal with tape cassettes in both a digital and analog fashion has presented several problems not only in the design of compatible hardware but, also, in the operating systems that can accept both kinds of data.
Thus, the problem solved by this invention relates to a magnetic tape cassette from which information must be read out in a digital fashion and a magnetic tape cassette which must be satisfactorily discriminated in an analog fashion to thereby carry out the digital reading or analog discrimination.